Electro-mechanical spatial light modulators have been designed for a variety of applications, including image processing, display, optical computing and printing. Electro-mechanical gratings for spatial light modulation are well known in the patent literature; see U.S. Pat. No. 5,311,360, issued May 10, 1994, to Bloom et al., entitled "Method and Apparatus for Modulating a Light Beam". This device, which is also known as a grating light valve (GLV), was later described by Bloom et al. with changes in the structure that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbon and substrate; 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast; 3) solid supports to fix alternate ribbons; and 4) an alternative device design that produced a blazed grating by rotation of suspended surfaces see U.S. Pat. No. 5,459,610, issued Oct. 17, 1995 to Bloom et al., entitled "Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate".
According to the prior art, for operation of the GLV device, an attractive electrostatic force is produced by a single polarity voltage difference between the ground plane and the conducting layer atop the ribbon layer. This attractive force changes the heights of the ribbons relative to the substrate. Modulation of the diffracted optical beam is obtained by appropriate choice of the voltage waveform. The voltage needed to actuate a ribbon a certain distance depends on several factors including the stress in the ribbon material, the distance between the ribbons and substrate, and the ribbon length.
It is well known that the ribbon elements of the GLV device possess a resonant frequency which depends primarily on the length of the ribbons and the density and tension of the ribbon material; see for example "Silicon Microfabrication of Grating Light Valves," Ph.D. Thesis, Stanford University 1995, Chapter 3, by F. S. A. Sandejas. When a ribbon is actuated or released, it rings at its resonant frequency, which is typically between 1 and 15 MHz. The mechanical response of the ribbon elements is damped by the surrounding gas as described in "Squeeze Film Damping of Double Supported Ribbons in Noble Gas Atmospheres," Proc. Of Solid-State Sensor and Actuator workshop, Hilton, Head, SC, June 8-11, 198, pp. 288-291. This damping depends on the type of gas present and pressure, and determines the width of the resonant peak associated with the resonant frequency of the ribbons. As a result of this resonant ringing, the maximum frequency at which the GLV device can be operated is limited, and the diffracted light intensity contains undesirable temporal variations. There is a need therefore for a GLV device having increased operating speed and reduced temporal light intensity variations.